<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>

    <style>
        * {
            margin: 0px;
            padding: 0px;
        }

        .clearfix:before, .clearfix:after {
            content: "";
            display: table;
        }

        .clearfix:after {
            clear: both;
        }

        .father {
            border: 1px solid red;
            width: 300px;
            background-color: pink;
        }

        .big {
            width: 100px;
            height: 100px;
            background-color: purple;
            float: left;
        }

        .small {
            width: 80px;
            height: 80px;
            background-color: blue;
            float: left;
        } 

         .footer {
            width: 400px;
            height: 100px;
            background-color: pink;
        } 
    </style>
</head>
<body>
    <div class="father clearfix">
        <div class="big"></div>
        <div class="small"></div>
    </div>

    <div class="footer"></div>
</body>
</html>